1. Field of the Invention
A number of tricyclic compounds find use in the treatment of depression. These tricyclic antidepressants include imipramine, desmethylimipramine (desipramine), amitriptyline, nortriptyline, protriptyline, doxepin and desmethyldoxepin (nordoxepin). In administering a tricyclic antidepressant, it is frequently necessary to ensure that the blood level of the antidepressant remains within a certain narrow concentration range in order to ensure effective dosage, while avoiding levels which may be toxic or produce undesirable effects. Furthermore, it is often necessary to detect potentially toxic levels of tricyclic antidepressants and their metabolites.
It is therefore desirable to provide a simple and rapid procedure for determining or detecting the levels of tricylic antidepressants in serum or other physiological fluids. The procedure should provide reproducible values and be specific for the tricyclic compounds which are measured. Thus, the procedure must be capable of distinguishing the tricyclic antidepressants from other drugs and from metabolites of the tricyclic antidepressant drug, which would otherwise give an erroneous result in any assay for the detection of tricyclic antidepressants.
Since the therapeutic range of the tricylic antidepressant drugs is from about 50 to 300 ng/ml, it is necessary not only to measure extremely small amounts of the tricyclic antidepressant drug in serum, but also to be able to distinguish between small differences in concentrations. Naturally occurring materials or metabolites of the tricyclic antidepressant drug in the serum sample may modify the observed signal so as to give falsely high results. It would therefore be desirable to provide for a simple means for pretreatment of a serum sample for a tricyclic antidepressant drug assay. The pretreatment method should be rapid and efficient and provide an assay sample containing the drug substantially free of interfering substances.
2. Brief Description of the Prior Art
The tricyclic antidepressants are closely related chemically to one another. Techniques reported for the determination of amitriptyline in biological fluids include the use of thin layer chromatography, gas-liquid chromatography and GLC-mass spectrometry. Gifford, et al., J. of Chrom., 105, 107-113 (1975); Gupta et al., Clin. Biochem., 9, 247-51 (1976); Nyberg and Martensson, J. Chromatography, 143, 491 (1977); Watson and Stewart, J. Chrom., 134, 182 (1977); ibid. 132 155-159 (1977). Radioimmunnoassay has been reported for amitriptyline by Aherne, et al., Br. J. Clin. Pharmac., 3, 561 (1976), Turner, Lancet, 180, 1316 (1977); and Aherne, et al., Lancet 1214 (1977). In Aherne, et al., ibid., a synthesis for an antigen for use as an immunogen for antibody formation is described, where nortriptyline is substituted with aminobutylene followed by conjugation to bovine serum albumin employing carbodiimide. In another antigen conjugate synthesis by Kaul, et al., J. Anal. Tox., 1, 236 (1977), nortriptyline was conjugated to bovine serum albumin through a succinyl group. The resulting antibodies were found to have significant cross-reactivity with a number of other tricyclic drugs.
U.S. Pat. No. 4,275,160 describes imipramine derivatives and poly(amino acid) conjugates. U.S. Pat. Nos. 4,223,013 and 4,307,245 disclose amitriptyline conjugates to antigenic proteins and enzymes.
N-(2-carboxyethyl) derivatives of nortriptyline and desipramine are disclosed by Hubbard et al., J. Pharm. Sc., 67, pp. 1571-1578 (1978) and by Hubbard et al., Canadian Journal of Pharmaceutical Sciences, 15, pp. 89-93 (1980).
Tricyclic antidepressant conjugates to antigens and enzymes are disclosed in U.S. patent application Ser. No. 522,887, filed Aug. 12, 1983.